Company work enclosure (4)
I believe the answer is:
coop
'enclosure' is the definition.
(coop is a kind of enclosure)
'company work' is the wordplay.
'company' becomes 'co' (abbreviation).
'work' becomes 'op' (operation, work done in an operating theatre).
'co'+'op'='COOP'
(Other definitions for coop that I've seen before include "pound" , "Birdcage" , "Store" , "Pen" , "box of chickens" .)